The extraordinary increase in agricultural productivity has been a result of many factors, including significantly better understanding of the methods involved with agriculture, improved equipment, availability of fertilizers, and improved pesticides. The latter factor has not been without detrimental aspects, however, due to the negative effect on the environment. There is, therefore, a substantial interest in developing effective and environmentally acceptable pesticides.
Among ecologically acceptable pesticides are the protein toxins produced by various microorganisms, such as Bacillus thuringiensis. However, the use of B. thuringiensis lysate or spores as a pesticide has significant drawbacks. The lifetime of the pesticide is relatively short in the environment, requiring multiple applications to give adequate protection. Consequently, these pesticides are not economical in comparison to more traditional chemical products having long residual activities. Improvements in field longevity would greatly aid in expanding the application of biological, or protein toxin-based pesticides.
West, Soil Biol. Biochem. (1984) 16:357-360 reports the results of a study on the persistence of B.t. toxin in soil. See also, West et al., J. of Invertebrate Pathology (1984) 43:150-155. U.S. Pat. No. 4,265,880 describes embedding live insecticidal pathogens in a coacervate microbead. Japanese Patent No. 51-5047 describes physical-chemical methods for killing B. thuringiensis spores, while retaining toxicity.